Constraint on the spatial distribution of the Early and Middle Jurassic units within the Nakatsugawa Complex of the North Kitakami Belt by detrital zircon U–Pb dating

Abstract

Previous detrital zircon U–Pb and fossil studies of the terrigenous rocks in the southwestern unit (Nakatsugawa Complex) of the North Kitakami Belt have suggested that the unit was formed during the Early to Middle Jurassic. In this study, we additionally performed detrital zircon U–Pb dating of two sandstones in the southwest part of the Nakatsugawa Complex (sample OM-07 and OM-06) for constraining the spatial distribution of the Early and Middle Jurassic units of the complex. As a result, those two samples showed youngest cluster ages of the middle and late Early Jurassic (183.3 ± 1.0 Ma in OM-07 and 176.7 ± 1.6 Ma in OM-06), respectively. Combining data from this and previous studies, we conclude that the unit from the southwestern margin to the location of OM-06 in the complex was formed during the Early Jurassic, while its northeastern part was formed during the Middle Jurassic. Moreover, it seems that the Nakatsugawa Complex has been formed without a significant age gap.